The invention concerns a process for the production of an expanded honeycomb core from foil band unwound from a band roll, coated with uniformly spaced strips of adhesive, and cut into strips in the direction of unrolling; the strips are piled on top of one another with their adhesive strips in a staggered arrangement, and are then adhesively bonded together under pressure. Subsequently the stack is expanded. The invention also concerns equipment for carrying out the process, and the use of the honeycomb core for the continuous production of a composite plate.
In the process conforming to GB-A-1 602 778 for the production of a honeycomb core, the foil is coated with strips of adhesive after unwinding from the band roll and longitudinally, i.e. in the direction of its unwinding. Then, a second foil treated in the same way is unwound from a second band roll and bonded to the first foil under pressure. Subsequently, from this intermittently produced, now two-layered foil band, strips of equal width are cut transversely to the unwinding direction, the width corresponding to the desired height of the honeycomb core. The strips are stacked with their adhesive strips staggered, bonded under pressure, and finally expanded.
In a similarly known process sheets are cut from the foil after unrolling from the band roll by cutting transversely to the unrolling direction. These are stacked with the adhesive strips applied in the unrolling direction in a staggered arrangement, and adhesively bonded under pressure. From the stacks so formed, strips of a width corresponding to the desired honeycomb core height are once again cut in the direction transverse to the direction of unwinding from the band roll, and these are further processed in the same way as in the previously described process.
To obtain accurate final dimensions of the honeycomb core, in both processes finishing machining by milling or similar is needed.
The honeycomb cores produced by these known processes have a honeycomb core width predetermined by the width of the foil bands and a honeycomb core length limited by the restricted number of strips or sheets to be stacked together. The band width amounts at most to about 180 cm, since wider foil bands are not obtainable, so that honeycomb core widths of only less than about 150 cm can be made. Moreover, particularly because of the need to ensure accuracy of the honeycomb core height by a separate machining operation such as milling or similar, the production is expensive and uneconomical because the above-mentioned cutting of the strips is not sufficiently accurate, since at the places where the adhesive is situated, the width of the strip packs is always narrower than at other points. In addition, from U.S. Pat. No. 3,655,475 a honeycomb core production process of the same general type is known, in which the foil width amounts to something more than twice the height of the eventual honeycomb core. The foil is coated on one side with evenly spaced adhesive strips transverse to the longitudinal direction, but with the outer zones and the middle of the foil free from adhesive. The adhesive strips are so arranged that there are strips over one-half of the foil width, while over the other half there are also strips, but in staggered positions with respect to those on the first half. The edge zones and the middle of the foil are free from adhesive strips. At one edge of the foil and close to the middle, but on the side opposite the edge in question, local precisely arranged perforations are made in the direction of unwinding and at the same height. The foil is then cut in the middle. The two resultant foil strips are then passed through an arrangement of rollers in such a way that they come to be positioned over one another with their adhesive strips in the same orientation, i.e. the front side of one foil strip lies against the back side of the other. To do this, the perforations are used to position the two strips so that the adhesive strips on one lie accurately half-way between those of the other. The pairs of strips are then stacked, bonded under pressure, and released by trimming off the adhesive-free edges.
Though, in contrast to the previously described processes, this procedure has the advantage of producing honeycomb cores of any desired width in principle, it suffers from the essential disadvantage that the trimming operation results inhigher wastage of foil material. Moreover, as in the previous cases, this additional machining makes it impossible to produce accurate final dimensions, for reasons already explained.
It is also known for honeycomb cores of the described type in the expanded condition to be joined together with covering layers on both sides, to form a composite material characterized by light weight and comparatively high strength. However, hitherto it has only been possible to produce such composites one piece at a time. Yet, there is a need to have stocks of a cheap honeycomb core with accurate final dimensions in a form that will allow the continuous production of composite plates. This necessitates at least a one-piece honeycomb core of practically any desired length.